#include <set>
#include <iostream>

int main()
{
    std::set<int> s;
    s.insert(1);
    s.insert(2);
    s.insert(3);

    for (const auto &i : s) {
        std::cout << i << std::endl;
    }

    s.erase(2);

    for (const auto &i : s) {
        std::cout << i << std::endl;
    }

    if (s.find(1) == s.end()) {
        std::cout << "connot find 1" << std::endl;
    } else {
        std::cout << "found 1" << std::endl;
    }

    if (s.find(2) == s.end()) {
        std::cout << "connot find 2" << std::endl;
    } else {
        std::cout << "found 2" << std::endl;
    }
    return 0;
}
